MILWAUKEE -- The F.B.I. is investigating a coordinated cyber attack that includes five banks, including J.P. Morgan Chase.

J.P. Morgan Chase Bank is the largest bank in the country, with assets of more than $2.5 trillion dollars. Thousands of account holders could be in jeopardy because of the attack, blamed on Russian hackers.

A report says the hackers targeted the systems of J.P. Morgan Chase and four institutions, taking a large amount of account information, including checking and savings account data. Only one of the banks affected by the attack has been made public. The report says it's unclear which other banks are involved, and that the attack could be retaliation for U.S. government-sponsored sanctions on Russia.